Why not get someone who's going to be a submissive instead of training someone to be? Might save a lot of hassle.
I am a submissive and I am also somewhat new to the role. I have been in relationships, where I have been the sub, but not like said out loud. She has to want the role. It is not something that can just be jumped into lightly. She has to be commited to it. It is something you are, not something to play around with. She needs to know her place! Good Luck!
Be patient but firm. You can ruin a submissive the way you can ruin a good dog by beating it to much. Communication is everything. Make the rules very clear. Try writing them down and having her sign them. Have her wright lines when she is bad. Praise her and reward her when she is good. It takes time but both of you will be happier should you succeed. Once she is trained she will be more valuable to you than any 10 women. Tell her this.